From nobody Sun Feb 8 03:27:28 2026 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8401E2D028A for ; Mon, 22 Dec 2025 14:09:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766412568; cv=none; b=OgKtY7kSZgd8TSEn/Xd3drx7kOArMfhvGJj172JsAAHovbsl7hU1T4bpfZb+LRrYQjosggDDiv3vEFuvQr36kOuhr4/VasGF7CKO+icUCDCkDWbhVyu//PdIrD0+Gne/vdgikcbFQewR8G9pcueXtS5B2m/bwXHM+PPLx3xaWQk= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766412568; c=relaxed/simple; bh=p/i6kMwISrCPM6iQXn0HaSNUzgsyoLTxQlFLGZ2uzQ8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=t5Kdkr0OmoM5y455RYve0lMx0spm5dQ5NYZoK0bWaU4VtRIwQk4mbj6ZnWZgUOTL+iiS/2cLqznNXh2Zq+/AeQyKH5UFNB2JVeyCGPG1YoRHCgFW6PJoXf/7RB9IZIkVEZ75CgKZtyGq+vWoUA9o+sCBdcfYc43dsVRa52fIj8Y= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=NqLrQ/gp; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b=pi2cVmg4; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="NqLrQ/gp"; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b="pi2cVmg4" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1766412564; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=k1FE0+YEZR+tBzsGFvPzgiyYjR1CkUcfeInMhZI6Of8=; b=NqLrQ/gp4dvpugfX/v8wHvmzXsAlBMwHALMmaeyE0NvG+agx1L9TTv5cbmt17j1ZyN7QiD peVb5bx5i0Fjoi4LvxMxv+qSX8oSuboYgZ+seIdnph0A3jQt32sUxRqFgcO1aTPvsdB2l/ bRUuMoTgRMRtXOJVjL1pH4AELhy7lf8= Received: from mail-wr1-f71.google.com (mail-wr1-f71.google.com [209.85.221.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-589-ovgmQU9_Me6FmuWiPhKH_Q-1; Mon, 22 Dec 2025 09:09:23 -0500 X-MC-Unique: ovgmQU9_Me6FmuWiPhKH_Q-1 X-Mimecast-MFC-AGG-ID: ovgmQU9_Me6FmuWiPhKH_Q_1766412562 Received: by mail-wr1-f71.google.com with SMTP id ffacd0b85a97d-430f433419aso3719339f8f.0 for ; Mon, 22 Dec 2025 06:09:22 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=google; t=1766412562; x=1767017362; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:autocrypt:content-language :from:references:cc:to:subject:user-agent:mime-version:date :message-id:from:to:cc:subject:date:message-id:reply-to; bh=k1FE0+YEZR+tBzsGFvPzgiyYjR1CkUcfeInMhZI6Of8=; b=pi2cVmg4E3/7T4cu7wjUDdh17qnTaSsG1JhvCC1B3CCsk8jr/fhEDNw1GCX42WtM8r XTYgUlByMOHgS1MeZuUx11EQx5iS1Bjg4/6JG/DBrITV2cVtxy3hF1TFHOqWfOp/WI9x GvffLmHb0FBmC8WOiHn2AdBxxJvSbXEZWyBcCa2LsOBrUwxSEDT6lwWYyeJTD4Iuz9aS HCXvNoQNtUZlumG6aEIlRpEGj1iE2BwO6zFLT5f5DG/uBOk1D3hMmcc4KFFhcF1HDwIT lvu40PVHBhgqwtve5Xs4gJfRGOJVGkpe+4bYC0t3aSCRUvtnEYKxRaDhv+SpB2NXLyr3 3i5A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1766412562; x=1767017362; h=content-transfer-encoding:in-reply-to:autocrypt:content-language :from:references:cc:to:subject:user-agent:mime-version:date :message-id:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=k1FE0+YEZR+tBzsGFvPzgiyYjR1CkUcfeInMhZI6Of8=; b=JcQHP+wgztVPAlFjQGMaDUG1dukDOn6zXfVcfI33R4bXC+wg5tTauJVGX+yIWVxa27 yegaW7TwtcSWAy3uU15/0M2yHS/FtQjP7/hkZg2tPKGp3rjSWAJkG0s0JXz/JR4N1z4x u0LL3nqudxCp2QsHlGf8ux5UqUtmbW4m4KyqkJaCUQUmVRfELednq5dM6i8pLK3/egnD 8/nPLGFMuPxxtRUHfjFM1NAi+YnKIH4nOY6U7WosLipUmQl/u+jaxyGALQw8DUHwob14 WVAycuyEmBcR/gQg0gmFWOjaJiqs/wHecuGuMYUNYkrMx6Enb/mc8XZQ6bFxWgXaJuMT eVwA== X-Forwarded-Encrypted: i=1; AJvYcCX6PgfKPEAZHSSVzSrc/yV+QeyRnXUieE3cNG7vbU0Zn0Unsx21nzFm+VIG4hvGAqDHBjbYOOYDqDeKBNc=@vger.kernel.org X-Gm-Message-State: AOJu0YzUgTsb9ZCj2W+p1nmI7O6TZjZSrjYc7bNG8pfhmPu+wQ0POqG5 xkKXADlx/JhYUoklT/mgW0/NcfVYc3PyjWAM5lgFR467yi12M+L9gE5YNJ8/6HvaBm/zVb++DBV YfeXDh+PU/OwNgp89fMOz+EnlEtAqriMKXYL1K7g9TtcniNjmVaOuoWw5Bl+3R3VL3g== X-Gm-Gg: AY/fxX7NbNi2BjPVkJ0tniS6IzAga3l/MsF13Tz46uiHrst/WmonIPolLvLeU3cD1+i 8/MD+FvQfHnUGmvi4NyWQDnHci/yaK9nd2mw9GqPMkfMPVutKmMliTfUrGeSJFb16Fes5gRiufP V0EtHWhu9SLL6VtjbE1h3iAGjZbDlfPboxkgtq1RI4vAQVImi95fTvl1bwtrStEW7+AeeaLt3mr +Ru6srKdYfEHoEYXWu/JKiSyQxzf00Kl0kTw/UoWl0Hl6GpY/XuTKFCSeYXzRpmaAglDvDiApNQ dXUQWNDrE87lS+ODvsfs9aJgafBEthHZ5hxuIfFi8q3OKxIZQDQfEzu9RxSZEAfHiht2tl9lEeR ybryksW89FIUQN16UPHxj3p2FAn0dbffxN/Wn7bTRTwg2roJ9rq/NQ4sGIRoFbqmWC4C7TBv0eq FgAXSvt5inOO8IbWQ= X-Received: by 2002:a05:6000:290b:b0:42f:f627:3a99 with SMTP id ffacd0b85a97d-4324e4fd929mr14060399f8f.38.1766412561895; Mon, 22 Dec 2025 06:09:21 -0800 (PST) X-Google-Smtp-Source: AGHT+IGP6HMp+dW+4S6ThYyhC4Zp8b5zu9Tx+uPg89UKRyiU9jj0V1LJEfNM5y7cCeqmYyTSzw3qRw== X-Received: by 2002:a05:6000:290b:b0:42f:f627:3a99 with SMTP id ffacd0b85a97d-4324e4fd929mr14060358f8f.38.1766412561414; Mon, 22 Dec 2025 06:09:21 -0800 (PST) Received: from [192.168.10.48] ([151.95.145.106]) by smtp.googlemail.com with ESMTPSA id ffacd0b85a97d-4324eaa2beasm21799471f8f.33.2025.12.22.06.09.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 22 Dec 2025 06:09:20 -0800 (PST) Message-ID: <42513cb3-3c2e-4aa8-b748-23b6656a5096@redhat.com> Date: Mon, 22 Dec 2025 15:09:13 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: possible deadlock due to irq_set_thread_affinity() calling into the scheduler (was Re: [PATCH v3 38/62] KVM: SVM: Take and hold ir_list_lock across IRTE updates in IOMMU) To: Ankit Soni , Sean Christopherson , Marc Zyngier Cc: Oliver Upton , Joerg Roedel , David Woodhouse , Lu Baolu , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, kvm@vger.kernel.org, iommu@lists.linux.dev, linux-kernel@vger.kernel.org, Sairaj Kodilkar , Vasant Hegde , Maxim Levitsky , Joao Martins , Francesco Lavra , David Matlack , Naveen Rao References: <20250611224604.313496-2-seanjc@google.com> <20250611224604.313496-40-seanjc@google.com> From: Paolo Bonzini Content-Language: en-US Autocrypt: addr=pbonzini@redhat.com; keydata= xsEhBFRCcBIBDqDGsz4K0zZun3jh+U6Z9wNGLKQ0kSFyjN38gMqU1SfP+TUNQepFHb/Gc0E2 CxXPkIBTvYY+ZPkoTh5xF9oS1jqI8iRLzouzF8yXs3QjQIZ2SfuCxSVwlV65jotcjD2FTN04 hVopm9llFijNZpVIOGUTqzM4U55sdsCcZUluWM6x4HSOdw5F5Utxfp1wOjD/v92Lrax0hjiX DResHSt48q+8FrZzY+AUbkUS+Jm34qjswdrgsC5uxeVcLkBgWLmov2kMaMROT0YmFY6A3m1S P/kXmHDXxhe23gKb3dgwxUTpENDBGcfEzrzilWueOeUWiOcWuFOed/C3SyijBx3Av/lbCsHU Vx6pMycNTdzU1BuAroB+Y3mNEuW56Yd44jlInzG2UOwt9XjjdKkJZ1g0P9dwptwLEgTEd3Fo UdhAQyRXGYO8oROiuh+RZ1lXp6AQ4ZjoyH8WLfTLf5g1EKCTc4C1sy1vQSdzIRu3rBIjAvnC tGZADei1IExLqB3uzXKzZ1BZ+Z8hnt2og9hb7H0y8diYfEk2w3R7wEr+Ehk5NQsT2MPI2QBd wEv1/Aj1DgUHZAHzG1QN9S8wNWQ6K9DqHZTBnI1hUlkp22zCSHK/6FwUCuYp1zcAEQEAAc0j UGFvbG8gQm9uemluaSA8cGJvbnppbmlAcmVkaGF0LmNvbT7CwU0EEwECACMFAlRCcBICGwMH CwkIBwMCAQYVCAIJCgsEFgIDAQIeAQIXgAAKCRB+FRAMzTZpsbceDp9IIN6BIA0Ol7MoB15E 11kRz/ewzryFY54tQlMnd4xxfH8MTQ/mm9I482YoSwPMdcWFAKnUX6Yo30tbLiNB8hzaHeRj jx12K+ptqYbg+cevgOtbLAlL9kNgLLcsGqC2829jBCUTVeMSZDrzS97ole/YEez2qFpPnTV0 VrRWClWVfYh+JfzpXmgyhbkuwUxNFk421s4Ajp3d8nPPFUGgBG5HOxzkAm7xb1cjAuJ+oi/K CHfkuN+fLZl/u3E/fw7vvOESApLU5o0icVXeakfSz0LsygEnekDbxPnE5af/9FEkXJD5EoYG SEahaEtgNrR4qsyxyAGYgZlS70vkSSYJ+iT2rrwEiDlo31MzRo6Ba2FfHBSJ7lcYdPT7bbk9 AO3hlNMhNdUhoQv7M5HsnqZ6unvSHOKmReNaS9egAGdRN0/GPDWr9wroyJ65ZNQsHl9nXBqE AukZNr5oJO5vxrYiAuuTSd6UI/xFkjtkzltG3mw5ao2bBpk/V/YuePrJsnPFHG7NhizrxttB nTuOSCMo45pfHQ+XYd5K1+Cv/NzZFNWscm5htJ0HznY+oOsZvHTyGz3v91pn51dkRYN0otqr bQ4tlFFuVjArBZcapSIe6NV8C4cEiSTOwE0EVEJx7gEIAMeHcVzuv2bp9HlWDp6+RkZe+vtl KwAHplb/WH59j2wyG8V6i33+6MlSSJMOFnYUCCL77bucx9uImI5nX24PIlqT+zasVEEVGSRF m8dgkcJDB7Tps0IkNrUi4yof3B3shR+vMY3i3Ip0e41zKx0CvlAhMOo6otaHmcxr35sWq1Jk tLkbn3wG+fPQCVudJJECvVQ//UAthSSEklA50QtD2sBkmQ14ZryEyTHQ+E42K3j2IUmOLriF dNr9NvE1QGmGyIcbw2NIVEBOK/GWxkS5+dmxM2iD4Jdaf2nSn3jlHjEXoPwpMs0KZsgdU0pP JQzMUMwmB1wM8JxovFlPYrhNT9MAEQEAAcLBMwQYAQIACQUCVEJx7gIbDAAKCRB+FRAMzTZp sadRDqCctLmYICZu4GSnie4lKXl+HqlLanpVMOoFNnWs9oRP47MbE2wv8OaYh5pNR9VVgyhD OG0AU7oidG36OeUlrFDTfnPYYSF/mPCxHttosyt8O5kabxnIPv2URuAxDByz+iVbL+RjKaGM GDph56ZTswlx75nZVtIukqzLAQ5fa8OALSGum0cFi4ptZUOhDNz1onz61klD6z3MODi0sBZN Aj6guB2L/+2ZwElZEeRBERRd/uommlYuToAXfNRdUwrwl9gRMiA0WSyTb190zneRRDfpSK5d usXnM/O+kr3Dm+Ui+UioPf6wgbn3T0o6I5BhVhs4h4hWmIW7iNhPjX1iybXfmb1gAFfjtHfL xRUr64svXpyfJMScIQtBAm0ihWPltXkyITA92ngCmPdHa6M1hMh4RDX+Jf1fiWubzp1voAg0 JBrdmNZSQDz0iKmSrx8xkoXYfA3bgtFN8WJH2xgFL28XnqY4M6dLhJwV3z08tPSRqYFm4NMP dRsn0/7oymhneL8RthIvjDDQ5ktUjMe8LtHr70OZE/TT88qvEdhiIVUogHdo4qBrk41+gGQh b906Dudw5YhTJFU3nC6bbF2nrLlB4C/XSiH76ZvqzV0Z/cAMBo5NF/w= In-Reply-To: Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8"; format="flowed" On 12/22/25 10:16, Ankit Soni wrote: > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D > WARNING: possible circular locking dependency detected > 6.19.0-rc2 #20 Tainted: G E > ------------------------------------------------------ > CPU 58/KVM/28597 is trying to acquire lock: > ff12c47d4b1f34c0 (&irq_desc_lock_class){-.-.}-{2:2}, at: __irq_get_d= esc_lock+0x58/0xa0 >=20 > but task is already holding lock: > ff12c49b28552110 (&svm->ir_list_lock){....}-{2:2}, at: avic_pi_updat= e_irte+0x147/0x270 [kvm_amd] >=20 > which lock already depends on the new lock. >=20 > Chain exists of: > &irq_desc_lock_class --> &rq->__lock --> &svm->ir_list_lock >=20 > Possible unsafe locking scenario: >=20 > CPU0 CPU1 > ---- ---- > lock(&svm->ir_list_lock); > lock(&rq->__lock); > lock(&svm->ir_list_lock); > lock(&irq_desc_lock_class); >=20 > *** DEADLOCK *** >=20 > So lockdep sees: >=20 > &irq_desc_lock_class -> &rq->__lock -> &svm->ir_list_lock >=20 > while avic_pi_update_irte() currently holds svm->ir_list_lock and then > takes irq_desc_lock via irq_set_vcpu_affinity(), which creates the > potential inversion. >=20 > - Is this lockdep warning expected/benign in this code path, or does it > indicate a real potential deadlock between svm->ir_list_lock and > irq_desc_lock with AVIC + irq_bypass + VFIO? I'd treat it as a potential (if unlikely) deadlock: (a) irq_set_thread_affinity triggers the scheduler via wake_up_process, while irq_desc->lock is taken (b) the scheduler calls into KVM with rq_lock taken, and KVM uses ir_list_lock within __avic_vcpu_load/__avic_vcpu_put (c) KVM wants to block scheduling for a while and uses ir_list_lock for that purpose, but then takes irq_set_vcpu_affinity takes irq_desc->lock. I don't think there's an alternative choice of lock for (c); and there's no easy way to pull the irq_desc->lock out of the IRQ subsystem--in fact the stickiness of the situation comes from rq->rq_lock and irq_desc->lock being both internal and not leaf. Of the three, the most sketchy is (a); notably, __setup_irq() calls wake_up_process outside desc->lock. Therefore I'd like so much to treat it as a kernel/irq/ bug; and the simplest (perhaps too simple...) fix is to drop the wake_up_process(). The only cost is extra latency on the next interrupt after an affinity change. diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c index 8b1b4c8a4f54..fc135bd079a4 100644 --- a/kernel/irq/manage.c +++ b/kernel/irq/manage.c @@ -189,14 +189,10 @@ static void irq_set_thread_affinity(struct irq_desc *= desc) struct irqaction *action; =20 for_each_action_of_desc(desc, action) { - if (action->thread) { + if (action->thread) set_bit(IRQTF_AFFINITY, &action->thread_flags); - wake_up_process(action->thread); - } - if (action->secondary && action->secondary->thread) { + if (action->secondary && action->secondary->thread) set_bit(IRQTF_AFFINITY, &action->secondary->thread_flags); - wake_up_process(action->secondary->thread); - } } } =20 Marc, what do you think? Paolo